Thread control in sewing machines is a very important consideration in the formation of a good stitch. In sewing machines employing oscillatory rocking loopers, a rotary thread take-up mechanism is usually employed to manipulate the looper thread as demanded by the oscillatory lengthwise movement of the looper. While the looper is moving toward the needle, the take-up mechanism allows a certain degree of slack in the thread system to allow the previous formed stitch to be set properly. During operation, the thread take-up mechanism is effective to create a loop in the looper thread so as to take-up the slack of the looper thread when the looper is returning to its initial position. During the return movement of the looper, and once all the slack has been removed from the system, the take-up mechanism is effective to pull or draw thread from the cone or supply source. Prior to the time the looper returns to its initial position, the looper thread will be "cast off" the high point of the looper thread take-up cam. After the thread has been cast off from the take-up cam, still further thread is delivered into the system between the take-up cam and the looper because of the continuing return motion of the looper. It should be noted that the required amount of looper thread for the next stitch was also drawn into the system before the thread was cast-off the high point of the take-up. To prevent the rotary thread take-up from drawing thread from the supply source, rather than from the looper on the return movement of the latter, it has been known to position a thread brake mechanism between the take-up mechanism and the thread supply. These thread brakes are effective only when the take-up mechanism is manipulating the looper thread into a loop during the reverse movement of the looper. During the withdrawal of the thread from the supply, the thread brake is open.
Such thread brake mechanisms have the disadvantage of not controlling the slack or excessive looper thread that results in the system once the looper thread is cast off from the take-up. It is when the looper thread is cast off from the take-up, thus resulting in an excessive amount of lose thread in the system that the looper thread has a tendency to wind around the take-up mechanism, thus drawing excessive amounts of thread from the supply. As mentioned, during this period of the cycle, the heretofor known thread brakes are ineffective and, thus, the thread is quickly spooled around the rotary shaft that is adapted to drive the take-up mechanisms. Before the machine is returned to operation, this wound up thread must be removed from the shaft to enable use of the machine. On many machines, the take-up area is inaccessible. Thus, the problem of removing the wound thread from about the rotary shaft is a timely and costly process.
The present invention involves a thread control mechanism which has the ability to apply a quick and effective clamping action to the sewing machine thread at an appropriate time interval so as to prevent the thread from winding around an operative rotary drive shaft of the machine. The clamping force magnitude of the instant invention may be selectively regulated to exceed the tensile strength of the thread. Thus, if thread is drawn from the supply as a result of it winding around the shaft, the present invention causes a break in the thread. In this manner, rather than drawing thread from the supply cone, the thread is torn or bursts and thread wind-up about an operative mechanism of the machine is eliminated. The instant thread control mechanism operates in timed relation with the stitch forming element of the machine so that it allows thread to be drawn from the supply when necessary and clamps same only when necessary. Thus, stitch formation is not affected by the present invention but a spooling up of the thread about an operable mechanism is eliminated.
The present invention includes a thread engaging member adapted to intermittently apply a clamping force to the thread. A circulatory moving actuator is effective to move a thread engaging member into contact with the thread in timed relation to the reciprocatory or oscillatory movements of the machine's stitch forming elements. The circulatory actuator may be in the form of an eccentric that is carried on the same shaft as the rotary disk take-up and, thus, may be set in timed relation thereto. Because loopers have different amounts of endwise travel and, thus, different thread demands, the clamping action and activation of the instant invention may require that various types of eccentrics be used according to the requirements of the thread and looper travel.
In line with all of the above, it is the primary object of this invention to provide suitable means which will prevent looper thread from spooling up about the looper thread take-up mechanism of the machine.
It is another object of this invention to provide a thread control mechanism which is relatively simple in construction, dependable in operation, and is suited in use in connection with industrial sewing machines.
Yet another object of this invention is to provide a thread control mechanism which is versatile for use with machines having various degrees of looper travel.